1. Technical Field
The present invention relates to a line head that scans a surface, such as a surface to be scanned, of a latent image carrier with light and an image forming apparatus using the same.
2. Related Art
A line head that scans a surface to be scanned of a photoconductor, which is a latent image carrier, with light to form a latent image has been used as a light source of an electrophotographic printer, which is an image forming apparatus.
An optical printer head, serving as a line head, includes a base plate, which is a substrate having light emitting diodes, serving as light-emitting elements, formed thereon, and a lens plate, which is a lens substrate that supports lenses. A lens array including lenses corresponding to the light emitting diodes is provided on the lens plate. When the base plate and the lens plate have different linear expansion coefficients and are heated, a positional deviation between the light emitting diode and the corresponding lens occurs, which makes it difficult to form a clear and exact latent image on a surface to be scanned of a photoconductor. Therefore, a structure in which the base plate and the lens plate have substantially the same linear expansion coefficient has been proposed (for example, see JP-A-6-270468 (page 3 and FIG. 1)
When the head substrate and the lens substrate have the same linear expansion coefficient, the positional relationship between the lens and the light-emitting element does not vary even though heat is applied. However, in this case, the focal position of light emitted from the light-emitting element on the surface to be scanned of the photoconductor is moved a distance corresponding to the amount of thermal expansion. When the line head is applied as an exposure unit to a tandem color image forming apparatus, the movement of the focal position causes a color registration error, and image quality deteriorates.